Mold assembly and method for manufacturing metal castings

ABSTRACT

A mold assembly for manufacturing a metal alloy casting includes a cope and drag mold, a plurality of sand cores and a pressure core. The cope mold includes an upper portion of a mold cavity. The drag mold includes a gating system, a lower portion of the mold cavity, and an upper portion of a plurality of riser cavities. The gating system is in communication with the riser cavities to provide pressurized liquid metal alloy to the riser cavities. The pressure core has a plurality of protrusions that are disposed in each of the upper portion of the plurality of riser cavities.

TECHNICAL FIELD

The present disclosure relates to metal casting processes and moreparticularly to aluminum alloy casting processes.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may or may not constitute priorart.

There are many different casting processes that produce high performancealuminum alloy cylinder heads. Gravity and low pressure permanent andsemi-permanent mold cast processes use sand cores for internal passagesand features. However, these processes tend to produce castings havinglower mechanical properties than could be achievable for the alloy.While castings made using tilt or rotating mold pouring mechanisms thatreduce metal turbulence have improved mechanical properties, theseprocesses tend to have a high associated cost due to long cycle timesand complexity of process and equipment.

Thus, some current aluminum alloy casting processes produce lessexpensive castings having low mechanical properties. Other processesproduce castings with high mechanical properties. However, for most ifnot all of these improvements come at an increased cost. Accordingly,there is a need in the art for an improved casting process that produceshigh quality, high performance aluminum castings at a lower, morecompetitive cost.

SUMMARY

The present invention provides a mold assembly for use in a method ofmanufacturing a metal alloy casting. The mold assembly comprises a copemold, a drag mold, a plurality of sand cores, and a pressure core. Thecope mold includes an upper portion of a mold cavity. The drag moldincludes a lower portion of the mold cavity and an upper portion of atleast a first riser cavity. The cope mold is disposed on top of the dragmold to combine the upper portion and lower portion of the mold cavity.The plurality of sand cores is disposed on the interior of the moldcavity of the cope and drag molds. The pressure core has at least afirst protrusion, and wherein the first protrusion is disposed adjacentto the first riser cavity and includes a top surface that forms a bottomportion of the first riser cavity.

In one embodiment of the present invention, the pressure core isdisposed in one of a first position and a second position. The firstriser cavity has a first volume when the pressure core is in the firstposition. The first riser cavity has a second volume when the pressurecore is in the second position. The second volume is less than the firstvolume.

In another embodiment of the present invention, the mold assemblyfurther includes a gating system and a piston core. The gating systemhas a runner in communication with the first riser cavity and the pistoncore is disposed in one of a first and a second position proximate tothe runner.

In yet another embodiment of the present invention, the first positionof the piston core allows for communication between the first risercavity and the runner and the second position of the piston coreinhibits communication between the first riser cavity and the runner.

In yet another embodiment of the present invention, the pressure core isa metal core.

In yet another embodiment of the present invention, the drag moldfurther includes a gating system that communicates liquid metal alloyfrom a pressurized source of liquid metal alloy to the riser cavities.

In yet another embodiment of the present invention, the pressurizedsource of liquid metal alloy includes one of an electromagnetic pump anda mechanical pump.

In yet another embodiment of the present invention, the pressurizedsource of liquid metal alloy includes a pouring basin and sprue.

In yet another embodiment of the present invention, the cope mold anddrag mold are permanent metal molds.

In yet another embodiment of the present invention, the pressure core isa movable portion of the drag mold.

The present invention also provides a mold assembly for use in a methodof manufacturing a metal alloy casting. The mold assembly comprises asand core assembly, a cope mold, and a drag mold. The sand core assemblyincludes at least a riser core and a piston core. The riser coreincludes a gating system and at least a first riser cavity. The pistoncore is disposed adjacent the first riser cavity. The cope mold includesan upper portion of a mold cavity. The drag mold includes a lowerportion of the mold cavity and a piston core actuator. The sand coreassembly is disposed in the lower portion of the mold cavity, the copemold is disposed on the drag mold, and the piston core actuator is fixedfor common movement with the piston core. The piston core is disposed inone of a first position and a second position. The first riser cavityhas a first volume when the piston core is in the first position. Thefirst riser cavity has a second volume when the piston core is in thesecond position. The second volume of the first riser cavity is lessthan the first volume of the first riser cavity.

In one embodiment of the present invention, the piston core has a topsurface that forms a portion of the first riser cavity.

In another embodiment of the present invention, the piston core includesa cross section having a width that is smaller than a cross section ofthe first riser cavity.

In yet another embodiment of the present invention, the pressurizedsource of liquid metal alloy includes one of an electromagnetic pump anda mechanical pump.

In yet another embodiment of the present invention, the pressurizedsource of liquid metal alloy includes and a pouring basin and sprue.

In yet another embodiment of the present invention, the mold assemblyfurther includes a second piston core. The gating system has a runner incommunication with the first riser cavity. The second piston core isdisposed proximate the runner in one of a first and a second position.The first position of the second piston core allows for communicationbetween the first riser cavity and the runner. The second position ofthe second piston core inhibits communication between the first risercavity and the runner.

The present invention also provides a method for manufacturing alightweight metal alloy casting. The method includes a first step ofproviding a mold assembly including an cope mold, a drag mold, and acore assembly forming a mold cavity, and wherein the drag mold includesat least a first riser cavity and a gating system, and wherein the firstriser cavity is at least partially formed by a movable first pistonactuator, and the runner is at least partially formed by a movablesecond piston actuator. A second step initializes filling the gatingsystem with a pressurized liquid metal alloy. A third step completesfilling the gating system, the first riser cavity, and mold cavity withthe pressurized liquid metal alloy. A fourth step discontinues fillingthe mold assembly with the pressurized liquid metal alloy and activatesthe second piston actuator to close the runner. A fifth step applies aforce to a bottom surface of the movable piston actuator mold in thedirection of the drag mold to increase the hydraulic pressure of theliquid metal alloy in the first riser cavity.

In one embodiment of the present invention, the method of furthercomprises extracting a solidified casting from the mold cavity andplacing the casting in an oven for heat treatment.

In another embodiment of the present invention, the method furthercomprises ejecting a solidified casting from the casting cavity.

In yet another embodiment of the present invention, the method furthercomprises placing the casting in an oven for heat treatment.

In yet another embodiment of the present invention, the step of applyinga force to a bottom surface of the movable piston actuator mold in thedirection of the drag mold to increase the hydraulic pressure of theliquid metal alloy in the first riser cavity further comprises applyinga force to a bottom surface of the movable piston actuator mold in thedirection of the drag mold, decreasing the volume of the first risercavity and increasing the hydraulic pressure of the liquid metal alloyin the first riser cavity.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a view of the head deck and combustion chambers of a cylinderhead casting according to the principles of the present invention;

FIG. 2 is a perspective view of a cylinder head casting according to theprinciples of the present invention;

FIG. 3 is a partially assembled view of a mold assembly according to theprinciples of the present invention;

FIG. 4A is an end view of a mold assembly according to the principles ofthe present invention;

FIG. 4B is a side view of a mold assembly according to the principles ofthe present invention;

FIG. 5 is a perspective cut-away view of a portion of a mold assemblyaccording to the principles of the principles of the present invention;

FIG. 6 is a section view of a portion of the mold assembly according tothe principles of the present invention;

FIGS. 7A-7C are section views of the interior of a mold assembly invarious stages of a casting method according to the principles of thepresent invention;

FIG. 8 is a section view of a portion of the mold assembly according tothe principles of the present invention,

FIG. 9 is a section view of a portion of the mold assembly according tothe principles of the present invention, and

FIG. 10 is a flowchart depicting a method of casting metal alloysaccording to the principles of the present invention.

DESCRIPTION

Referring to the drawings, wherein like reference numbers refer to likecomponents, in FIGS. 1 and 2 an aluminum alloy cylinder head 10 producedusing a metal alloy casting method 100 is illustrated in accordance withan example of the present invention and will now be described. Ingeneral, the cylinder head 10 includes features such as a head deck 12,combustion chambers 14, intake and exhaust ports 16, camshaft bearings18, spark plug holes 20, water jacket openings 22, and oil passages 24,among other features. More particularly, the important features of thecylinder head 10 that are at least partially formed during the castingprocess include the head deck 12 and combustion chambers 14. Productspecifications for the head deck 12 and combustion chambers 14 generallyrequire higher yield and tensile strength than other areas of thecylinder head 10. Furthermore, improving cooling rates locally can beachieved with less effort than improving cooling rates in the entiretyof the casting. For example, faster cooling rates of the head deck andcombustion chambers produce finer microstructure; approximately 20 μmdendritic arm spacing (DAS), and higher strengths. Other areas of thecylinder head 10 that cool at a slower rate may result in DAS of about60 μm. Additionally, mechanical properties can be improved by othermeans such as providing pressurized liquid metal to areas of the castingthat solidify last. This results in improved microstructure by reducingporosity and shrinkage defects.

Turning now to FIG. 3, a mold assembly 30 used in a casting method toproduce cylinder heads 10 according to the present invention isillustrated and will now be described. The particular mold assembly 30of FIG. 3 produces two cylinder head 10 castings in a mold cavity 8formed by a number of sand cores 32 and sand molds 34. However, certainexterior features of the cylinder head 10 casting may be formed usingsand or metal molds 34. For example, the molds 34 may be made from toolsteel and fitted with hydraulic actuators to provide improved mechanicalproperties and reusable or permanent molds 34.

The sand cores 32 form part of the exterior features and all theinterior features of the cylinder head 10 casting and include, forexample, two end cores 36, two side cores 38, two center cores 40, twohead cover cores 42, two exhaust port cores 44, two intake port cores46, two water jacket cores 48, and two oil drain cores 50. The molds 34include a lower or drag mold 62, an upper or cope mold 64, and apressure core or mold 76. During assembly of the mold assembly 30, thesand cores 32 are inserted in a specified order into the drag mold 62 orthe cope mold 64. In the example shown in FIGS. 3, 4A, and 4B, the sandcores 32 are placed in the drag mold 62 with the cope mold 64 placed ontop of the assembled sand cores 32 thus securing the sand cores 32 inplace. In some embodiments, the sand cores 32 are assembled into a corepackage prior to placing the core package into the drag mold 62. Inother embodiments, the sand cores 32 may require adhesive, screws, andother retention mechanisms to hold the sand cores 32 in place. However,such practices are within the scope of the present invention. Detailsregarding the pressure core or mold 76 are explained in more detailbelow.

In the present invention, the included features of the drag mold 62 areof particular interest. The drag mold 62 includes a gating system 66formed for receiving liquid metal from a pressurized liquid metal alloysource and directing the liquid metal alloy to the cavities formedtherein by the sand cores 32 and sand molds 34 of the mold assembly 30.While a portion of the gating system 66 is viewable in FIG. 3, thegating system 66 is shown in more detail in FIGS. 4A, 4B, 5, and 6. Thegating system 66 of the drag mold 62 includes an inlet 68, a pluralityof runners or runners 70, and a plurality of riser cavities 72. Morespecifically, the inlet 68 receives the liquid metal alloy from apressurized liquid metal alloy source such as an electromagnetic ormechanical pump. Another mechanism that may be used to providepressurized liquid metal alloy to the inlet 68 includes a feature formedin the mold assembly 30 having a pouring basin 86 and a sprue 88, asshown in FIG. 4B. Independent of the means of providing pressurizedliquid metal alloy to the inlet 68, the inlet 68 transfers the liquidmetal to the runners 70. The runners 70 are in communication with andfeed liquid metal to the plurality of riser cavities 72. The runners 70control the flow rate and turbulence of the liquid metal by controllingthe diameter and shape of the runners 70. The riser cavities 72 arefilled with the liquid metal starting at the bottom of the risercavities 72 and in turn fill the mold cavity 8 of the mold assembly 30as the liquid metal rises into the casting cavities formed by the spacebetween the sand cores 32 and the molds 34.

Referring now to FIG. 6, the core structure used in the formation of theriser cavities 72 is illustrated and will now be described. The risercavity includes an upper portion 82 and a lower portion 83. The upperportion 82 of the riser cavity 72 is formed in the drag mold 62 whilethe lower portion 83 of the riser cavity is formed by the pressure core76. The upper and lower portions 82, 83 of the riser cavities 72 formthe cavity that produces the risers 72 when the liquid metal alloy isintroduced into the mold assembly 10. The pressure core 76 includes aplurality of protrusions 78 each extending into the cavity 82 of thedrag mold 62. In other embodiments, multiple pressure cores having asingle protrusion may be incorporated into the mold assembly 10.Regardless of the configuration of the pressure core 76, what isnecessary is for the protrusions 78 to move relative to the drag mold62. As shown in FIG. 6, the upper portion 82 of the riser cavity 72 isshaped like a bullet, however, other shapes or configurations of theriser cavity may be contemplated without departing from the scope of theinvention. For example, a riser cavity 72 may be a continuous cavityshape that extends from a cover rail of a cylinder head. In the presentembodiment, the protrusions 78 of the pressure core 76 have acylindrical shape with a smaller diameter D than that of the upperportion 82 of the riser cavity 76. In other embodiments, multiplepressure cores having a single protrusion may be incorporated into themold assembly 10. Regardless of the configuration of the pressure core76, the constant among all embodiments is that the protrusions 78 arecapable of relative movement to the drag mold 62.

Each of the plurality of protrusions 78 includes a top surface 84 thatforms the bottom portion 83 of the riser cavities 72. The protrusions 78are fitted into the upper portion 82 of the riser cavities 72 and arecapable of movement within the cavities 82 in an upward direction Y.More particularly, the pressure core 76 is capable of being manipulatedinto at least two positions. In a first position, detailed in FIGS. 7Aand 7B, the pressure core 76 is disposed such that the riser cavities 72have a first volume. In a second position, detailed in FIG. 7C, a forceY is applied to the pressure core 76 so that the pressure core 76 isdisposed such that the riser cavities 72 have a second volume which isless than the first volume. The reduction in volume between the firstand the second positions translates to an increase in pressure of theliquid metal alloy in the casting cavity, explained in more detailbelow. Furthermore, it is preferable that the protrusions 78 are beingforced into a volume of the riser cavity 72 that is still mostly liquidso as to increase the pressure of the liquid in the riser cavity 72 andsubsequently in the mold cavity 8.

With continuing reference to FIGS. 7A, 7B, and 7C, a series of figuresdepicting progressive stages of the manufacturing of cast alloy cylinderheads 10 are illustrated and will now be described. After the moldassembly 30 is inspected and assembled, the mold assembly 30 is insertedinto a machine and secured by hydraulic clamping mechanisms such thatthe drag mold 62 of the mold assembly 30, and therefore the gatingsystem 66, is the lower portion of the mold assembly 30. A pressurizedsource of liquid metal alloy (not shown) is provided to the inlet 68 ofthe gating system 66. As the liquid metal alloy is introduced to thegating system 66, the liquid metal alloy first fills the runner 70 andrisers 72 before reaching the mold cavity 8, as in FIG. 7A. As theliquid metal alloy continues to enter the gating system 66, the level ofthe liquid metal alloy rises through the risers 72 and begins to fillthe mold cavity 8, as in FIG. 7B. In FIG. 7C, the liquid metal alloycompletely fills the mold cavity 8 and the machine applies a force tothe pressure cores 76 in the upward direction Y while holding the moldassembly 30 as a whole in the same position. At this point in theprocess, the metal alloy in the top portion of the mold cavity 8 isstarting to solidify while the last liquid metal alloy that enters themold assembly 30 is hottest and remains liquid. As the metal in the moldcavity 8 solidifies, additional liquid metal is required to inhibitporosity or shrinkage defects. Thus, the application of pressure in therisers 72 by the pressure core 76 promotes the feeding of additionalliquid metal alloy to the mold cavity 8 as the first metal in the moldcavity 8 solidifies. The additional liquid metal feeds the voids formedby the contracting solidification of the first metal in the mold cavity8.

With reference to FIG. 8, another embodiment of the present inventionincluding an alternative core and mold assembly 100 is illustrated andwill now be described. In this particular example, a riser cavity 102 isformed by a metal mold 104 and several sand cores, including, a risercore 106, a base core 108, and a piston core 110. More specifically, theriser core 106, base core 108 and piston core 110 are assembled to forma riser cavity 112 and placed within the metal mold 104. In oneembodiment, the piston core 110 may be made as a breakaway portion ofthe base core 108. Furthermore, the metal mold 104 may be a mold for asemi-permanent mold machine or any one of several mold machines orprocesses utilizing a metal mold 104 without departing from the scope ofthe invention.

The riser cavity 112 includes an upper portion 114 and a lower portion116. The upper portion 114 of the riser cavity 112 is formed in theriser core 106 while the lower portion 116 of the riser cavity is formedpartially by the base core 108 and the piston core 110. The riser core106 also includes a portion of the gating system 118 that provides apath for the liquid metal alloy to communicate between the source of thepressurized liquid metal alloy and the riser cavity 112. The upper andlower portions 114, 116 of the riser cavity 112 form to cast the risers72 when the pressurized liquid metal alloy is introduced into the coreand mold assembly 100.

The metal mold 104 includes a piston core actuator 120 having a topsurface 122 on which is disposed the piston core 110. The piston coreactuator 120 and the piston core 110 are capable of relative movementwith the metal mold 104 and the base core 108. In one embodiment, thepiston core 110 and the base core 108 may be made as a connected singlecore with the piston core 110 being designed as a breakaway portion ofthe base core 108. The piston core actuator 120 is further fixed to ahydraulic slide (not shown) or other force inducing mechanism thatapplies a force P to the piston core actuator 120.

In one example of the present invention, multiple piston cores 110 andriser cavities 112 are included in the core and mold assembly 100 as isrequired by the design of the casting. Regardless of the configurationand number of piston cores 110 and riser cavities 112, what is necessaryis for the piston cores 110 to move relative to the riser cavities 112.The piston core 110, as shown in FIG. 8, has a cross section X that issignificantly smaller than the cross section Y of the riser cavity 112.This allows for the piston core 112 to move into the riser cavity 112without contacting metal alloy closer to the core surfaces that might bealready solidified.

Turning now to FIG. 9, another embodiment of the present inventionincluding an alternative core and mold assembly 100 is illustrated andwill now be described. Some features of FIG. 9 include carryoverreference numbers of similar features from previous FIGS. In thisexample, the gating system 118 includes a runner 124 that communicatespressurized liquid metal alloy through the gating system 118 from theinlet 68 to the riser cavities 112. The runner 124 is formed by themetal mold 104 and several sand cores, including, a riser or cope core106, a base or drag core 108, and a piston core 110. More specifically,the cope core 106, drag core 108 and piston core 110 are assembled toform a runner 112 and placed within the metal mold 104. In oneembodiment, the piston core 110 may be made as a breakaway portion ofthe drag core 108. Furthermore, the metal mold 104 may be a mold for asemi-permanent mold machine or any one of several mold machines orprocesses utilizing a metal mold 104 without departing from the scope ofthe invention.

The metal mold 104 includes a piston core actuator 126 having a topsurface 128 on which is disposed the piston core 110. This embodimentmay be included in several of the gating systems 118 runners 124throughout the mold assembly 100. The piston core actuator 126 and thepiston core 110 are capable of relative movement with the metal mold 104and the drag core 108. In one embodiment, the piston core 110 and thebase core 108 may be made as a connected single core with the pistoncore 110 being designed as a breakaway portion of the base core 108. Thepiston core actuator 120 is further fixed to a hydraulic slide (notshown) or other force inducing mechanism that applies a force F to thepiston core actuator 120. The piston core 110, when engaged by thepiston core actuator 120, moves into the runner 124 effectively blockingthe runner 124 and preventing any additional flow of liquid metal alloyfrom flowing in either direction in the runner 124. The piston coreactuator 120 in this embodiment may operate independently form thepiston core actuator 120 of the embodiment shown in FIG. 8.

Referring now to FIG. 10, a flowchart depicting a method 200 formanufacturing cast alloy cylinder heads 10 is illustrated and will nowbe described. The method 200 begins with a first step 202 of providing amold assembly 30. The mold assembly 30 includes a drag or lower mold 62having a gating system 66 formed therein and a pressure core 76, a copeor upper mold 64, and a plurality of sand cores 32. A second step 204begins to fill the gating system 66 and mold cavity 8 with pressurizedliquid metal alloy. A third step 206 completes filling the mold cavity 8or partially fills the mold cavity 8. A fourth step 208 discontinuesfilling the system with pressurized liquid metal alloy and engages thepiston core actuator 120 effectively closing the runner 118 leading tothe riser cavities 112. Alternatively, the runner 118 freezes to preventbackflow of liquid metal alloy from the riser cavity 72. A fifth step210 applies a force to the bottom surface of the pressure core 76 in theupward direction Y to pressurize the liquid metal alloy in the risercavity 72 thus forcing liquid metal alloy into any voids formed in thesolidification of the metal alloy in the mold cavity 8. A sixth step 212places the mold assembly 30 in an oven for sand removal and heattreatment. Alternatively, a seventh step 214 ejects the casting from themold cavity 8, removes the gating system and risers from the casting,cleans sand cores from the internal passages of the casting, and heattreats the casting.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and examples for practicingthe invention within the scope of the appended claims.

The following is claimed:
 1. A mold assembly for manufacturing a metalalloy casting, the mold assembly comprising; a cope mold including anupper portion of a mold cavity; a drag mold including a lower portion ofthe mold cavity and an upper portion of at least a first riser cavity,and wherein the cope mold is disposed on top of the drag mold to combinethe upper portion and lower portion of the mold cavity; a plurality ofsand cores disposed on the interior of the mold cavity of the cope anddrag molds, and a pressure core having at least a first protrusion, andwherein the first protrusion is disposed adjacent to the first risercavity and includes a top surface that forms a bottom portion of thefirst riser cavity.
 2. The mold assembly of claim 1 wherein the pressurecore is disposed in one of a first position and a second position, andwherein the first riser cavity has a first volume when the pressure coreis in the first position, and the first riser cavity has a second volumewhen the pressure core is in the second position, and the second volumeis less than the first volume.
 3. The mold assembly of claim 1 furtherincluding a gating system and a piston core, and wherein the gatingsystem has a runner in communication with the first riser cavity and thepiston core is disposed in one of a first and a second position.
 4. Themold assembly of claim 3 wherein the first position of the piston coreallows for communication between the first riser cavity and the runnerand the second position of the piston core inhibits communicationbetween the first riser cavity and the runner.
 5. The mold assembly ofclaim 1 wherein the drag mold further includes a gating system thatcommunicates liquid metal alloy from a pressurized source of liquidmetal alloy to the riser cavities.
 6. The mold assembly of claim 5wherein the pressurized source of liquid metal alloy includes one of anelectromagnetic pump, a mechanical pump, and a low-pressure furnace. 7.The mold assembly of claim 5 wherein the pressurized source of liquidmetal alloy includes a pouring basin and sprue.
 8. The mold assembly ofclaim 1 wherein the cope mold and drag mold are permanent metal molds.9. The mold assembly of claim 8 wherein the pressure core is a movableportion of the drag mold.
 10. A mold assembly for manufacturing a metalalloy casting, the mold assembly comprising; a sand core assembly havinga riser core and a first piston core, and wherein the riser coreincludes a gating system and at least a first riser cavity and the firstpiston core is disposed adjacent the first riser cavity; a cope moldincluding an upper portion of a mold cavity; a drag mold including alower portion of the mold cavity and a first piston core actuator, andwherein the sand core assembly is disposed in the lower portion of themold cavity, the cope mold is disposed on the drag mold, and the firstpiston core actuator is fixed for common movement with the piston core;wherein the first piston core is disposed in one of a first position anda second position, and wherein the first riser cavity has a first volumewhen the first piston core is in the first position, and the first risercavity has a second volume when the first piston core is in the secondposition, and the second volume of the first riser cavity is less thanthe first volume of the first riser cavity.
 11. The mold assembly ofclaim 10 wherein the first piston core has a top surface that forms aportion of the first riser cavity.
 12. The mold assembly of claim 11wherein the first piston core includes a cross section having a widththat is smaller than a cross section of the first riser cavity.
 13. Themold assembly of claim 10 wherein the pressurized source of liquid metalalloy includes one of an electromagnetic pump, a mechanical pump, and alow-pressure furnace.
 14. The mold assembly of claim 10 wherein thepressurized source of liquid metal alloy includes a pouring basin andsprue.
 15. The mold assembly of claim 10 further including a secondpiston core, and wherein the gating system has a runner in communicationwith the first riser cavity, the second piston core is disposedproximate the runner in one of a first and a second position, the firstposition of the second piston core allows for communication between thefirst riser cavity and the runner and the second position of the secondpiston core inhibits communication between the first riser cavity andthe runner.
 16. A method for manufacturing a lightweight metal alloycasting, the method comprising: providing a mold assembly including ancope mold, a drag mold, and a core assembly forming a mold cavity, andwherein the drag mold includes at least a first riser cavity and agating system, and wherein the first riser cavity is at least partiallyformed by a movable first piston actuator, and the runner is at leastpartially formed by a movable second piston actuator; initializingfilling the gating system with a pressurized liquid metal alloy;completing filling the gating system, the first riser cavity, and moldcavity with the pressurized liquid metal alloy; discontinuing fillingthe mold assembly with the pressurized liquid metal alloy and activatingthe second piston actuator to close the runner; applying a force to abottom surface of the movable piston actuator mold in the direction ofthe drag mold and increasing the hydraulic pressure of the liquid metalalloy in the first riser cavity.
 17. The method of claim 16 furthercomprises extracting a solidified casting from the mold cavity andplacing the casting in an oven for heat treatment.
 18. The method ofclaim 17 further comprises ejecting a solidified casting from thecasting cavity.
 19. The method of claim 18 further comprises placing thecasting in an oven for heat treatment.
 20. The method of claim 16applying a force to a bottom surface of the movable piston actuator moldin the direction of the drag mold to increase the hydraulic pressure ofthe liquid metal alloy in the first riser cavity further comprisesapplying a force to a bottom surface of the movable piston actuator moldin the direction of the drag mold, decreasing the volume of the firstriser cavity and increasing the hydraulic pressure of the liquid metalalloy in the first riser cavity.